Referring to FIG. 1, a single refrigerant refrigeration system includes a compressor 11, a condenser 12 disposed downstream of and fluidly connected to the compressor 11, an expansion valve 13 disposed downstream of and fluidly connected to the condenser 12, and an evaporator 14 disposed downstream of the expansion valve 13 and upstream of the compressor 11.
During operation of the refrigeration system, a refrigerant 101 flows into the compressor 11 and is compressed into a high-temperature and high-pressure gasified refrigerant 101, after which it flows into the condenser 12 and is condensed into a normal-temperature and high-pressure liquefied refrigerant 101. Next, the normal-temperature and high-pressure liquefied refrigerant 101 flows into the expansion valve 13 and is converted into a low-temperature and low-pressure liquefied refrigerant 101. Afterwards, the low-temperature and low-pressure liquefied refrigerant 101 flows into the evaporator 14, absorbs heat, and is converted into a low-temperature and low pressure gasified refrigerant 101 which then flows back into the compressor 11. The existing single refrigerant refrigeration system is generally used in an air conditioning system and a refrigeration system. However, the cooling temperature of the existing single refrigerant refrigeration system ranges between 10° C. and 30° C. If a lower temperature refrigeration system is required, a dual refrigerant refrigeration system must be used.
Referring to FIG. 2, an existing dual refrigerant refrigeration system includes a liquefaction unit 15 and a cooling unit 16. The liquefaction unit 15 includes a liquefaction compressor 151, a liquefaction condenser 152 fluidly connected to the liquefaction compressor 151, a liquefaction expansion valve 153 fluidly connected to the liquefaction condenser 152, and a heat exchanger 154 fluidly interconnecting the liquefaction expansion valve 153 and the liquefaction compressor 151. The cooling unit 16 includes a cooling compressor 161 fluidly connected to the heat exchanger 154, a cooling expansion valve 162 fluidly connected to the heat exchanger 154, and a cooling evaporator 163 fluidly connected to the cooling expansion valve 162 and the cooling compressor 161.
The liquefaction unit 15 uses, for example, R404A or R507 refrigerant 105, which can be liquefied at high pressure and normal temperature. The cooling unit 16 uses, for example, R23 refrigerant 106, which cannot be liquefied at high pressure and normal temperature. By virtue of the heat exchanger 154, the refrigerant 105 of the liquefaction unit 15 can liquefy the refrigerant 106 of the cooling unit 16 so that the refrigeration system can provide a cooling temperature of about −85° C.
When a wide range of the cooling temperature is required, the existing practice is to equip the refrigeration system with the single refrigerant refrigeration system and the dual refrigerant refrigeration system simultaneously. However, the production and maintenance costs of these two refrigeration systems are not only relatively high, but also they occupy a substantial space.